Circuit arrangement and method for attenuation compensation in an antenna signal link

ABSTRACT

A circuit arrangement for compensating for an attenuation occurring in an antenna signal link between a mobile radio terminal and an antenna has at least one antenna signal amplifier in the antenna signal link and a control unit for adjusting a gain factor. The antenna signal conducted through an associated antenna signal amplifier is amplified or attenuated. The circuit arrangement has a detection unit for detecting an antenna signal power (P M , P A ) of the antenna signal in the signal path of the antenna signal link. The control unit is configured for changing the gain factor, detecting a change, changing the transmit power (P M ) of the mobile radio terminal, and adapting the gain factor to the coupling attenuation of the antenna signal link in dependence on a detected response of the mobile radio terminal.

FIELD OF THE INVENTION

The invention relates to a circuit arrangement for compensating for anattenuation occurring in an antenna signal link between a mobile radioterminal and an antenna comprising at least one antenna signal amplifierin the antenna signal link and with a control unit for adjusting a gainfactor, by which the antenna signal conducted through an associatedantenna signal amplifier is amplified or attenuated, wherein the circuitarrangement has at least one detection unit for detecting an antennasignal power of the antenna signal in the signal path of the antennasignal link.

The invention also relates to a method for compensating for anattenuation occurring in an antenna signal link between a mobile radioterminal and an antenna with the aid of at least one signal amplifier inthe antenna signal link, having the step of detecting an antenna signalpower of the antenna signal in the signal path of the antenna signallink.

BACKGROUND

When a mobile radio terminal is connected to an external antenna astakes place, e.g. with hands-free facilities in motor vehicles,attenuation occurs on the signal path from the mobile radio terminal tothe antenna and conversely. Although the quality of transmission andreception is to be improved by the external antenna, the attenuation hasthe effect that the maximum possible signal quality is not achieved.

In practice, the attenuation is approximately constant in the case of acable-connected linking of the mobile radio terminal to the antenna andenables a compensation circuit having a constant gain factor to beoperated. In the case of an electromagnetic capacitive or inductivecoupling of the mobile radio terminal to the antenna signal amplifierand the antenna connected thereto, however, the attenuation can vary independence on the current operating state and the mobile radio terminalused. A predetermined constant gain factor is then not optimal forcompensating for the instantaneous attenuation.

DE 10 2013 101 590 A1 describes a circuit arrangement for compensatingfor coupling attenuation in an antenna signal link in which a gainfactor is adapted at a rate of change which is slower compared with thenormal speed of an antenna signal power control loop between a connectedmobile radio terminal and a base station of a mobile radio network. Dueto the power control on the network side, however, the signal power ofthe mobile radio terminal is, in any case, first adapted to the presenttotal attenuation between mobile radio terminal and base station so thatthe mobile radio terminals transmit with the minimal possible (optimal)power. This power control on the network side is supported by anadditional adaptation of the gain factor for a predetermined limitrange.

SUMMARY

On the basis of this, it is the object of the present invention tocreate an improved circuit arrangement for compensating for anattenuation occurring in an antenna signal link between a mobile radioterminal and an antenna and a compensation method therefor by means ofwhich an adjustment of the gain factor, adapted to the operating state,of the at least one antenna signal amplifier takes place in a simplemanner without access to information of the mobile radio terminal andwithout elaborate surveying of the coupling attenuation actuallycurrently present.

The object is achieved by the circuit arrangement having the features ofclaim 1 and by the compensation method having the features of claim 11.Advantageous embodiments are described in the subclaims.

It is proposed that the control unit of the circuit arrangement isconfigured for changing the gain factor, for detecting a change in theantenna signal power following as response thereto by changing thetransmitting power of the mobile radio terminal, i.e. by the change inthe antenna signal power through a power control of the mobile radioterminal then starting effectively, and for adapting the gain factor tothe coupling attenuation of the antenna signal link in dependence on adetected response of the mobile radio terminal.

Thus, for example, there is no need for adapting the gain factor whenthe transmit signal power of the mobile radio terminal responds to achange in the gain factor performed by way of a test and, as a result,the antenna signal power of the compensator thus remains unchanged. Thisis then an indication that the power control on the network side canperform the compensation of the coupling attenuation and thus there is agood reception.

If, in contrast, the transmit signal power of the mobile radio terminaldoes not change with a change in the gain factor, then the power controlon the network side of the mobile radio terminal by the base stationconnected thereto is no longer effective. This means that the mobiletelephone has reached its maximum transmitting power. This applies, inparticular, if the mobile radio terminal is sending with the maximumtransmit power. The detected antenna signal power will then change,however, in accordance with the change of the gain factor since it is nolonger influenced by a response of the power control of the mobile radioterminal. The lack of a response of the mobile radio terminal thus leadsto a detectable response of the antenna signal power of the antennasignal, particularly of the output signal power of the circuitarrangement which is detected by the detection unit. If such a responseis detected, this then enables the gain factor to be adapted in such amanner that a compensation of the coupling attenuation takes place. Inthis context it is necessary, e.g., to compensate for a differencebetween the predetermined maximum antenna signal power and the antennasignal power which has been detected before the change in the gainfactor, by correspondingly changing the gain factor.

In this context, the control unit can be configured for a furtherincrease in the gain factor if, by detecting the antenna signal power,no change of the transmit signal power of the mobile radio terminal asresponse to a test-wise increase in the gain factor is detected. By thismeans, the transmit signal power of the mobile radio terminal isevaluated. In this state, the precise coupling attenuation is thencalculated and the missing gain is set so that the coupling attenuationis compensated for, as a result of which the output power of the circuitarrangement thus corresponds to the output power of the mobile radioterminal. Optionally, however, it is also possible to increase the gainfactor incrementally without calculation (possibly by an estimate) ofthe coupling attenuation to such an extent until the maximum outputpower is achieved (slow approach). This is the case when the outputsignal power of the circuit arrangement approaches the transmit signalpower of the mobile radio terminal remaining the same with the increasein the gain factor.

The control unit can be configured for adjusting a predetermined minimumgain factor if the detected antenna signal power is less than apredetermined threshold value. By this means, an operation with thepredetermined minimum gain factor is performed within a range determinedby the predetermined threshold value, at which gain factor the powercontrol on the network side is adequate for compensating for couplingattenuations in the antenna signal path. It is only when the detectedantenna signal power such as, for example, the output signal power ofthe compensation circuit arrangement and particularly the output signalpower of the antenna signal of the antenna signal amplifier conducted tothe antenna corresponds to the threshold value or exceeds it that it isdecided, e.g. by test-wise changing of the gain factor by means of theresultant response either due to a starting power control of the mobileradio terminal or by absence of the power control of the mobile radioterminal whether and to what extent there is an adaptation of the gainfactor. In the case where the power control on the network side can nolonger become effective since the mobile radio terminal has reached itsmaximum possible transmit signal power, the detected transmit signalpower remains constant in spite of adaptation of the gain factor. Thisthen makes it possible to infer the actually existing couplingattenuation in the antenna signal path on the basis of the detectedantenna signal power.

In principle, the gain factor can be adjusted to the predeterminedminimum gain factor V_(min) under the following criteria which areselectable separately or in combination:

-   -   a) generally on detection of a change in the transmit signal        power;    -   b) if the detected antenna signal power is less than a        predetermined threshold value, particularly before the first        determination of the optimum gain factor V_(opt);    -   c) if the detected antenna signal power is less than a        predetermined second threshold value after the first        determination of the optimum gain factor V_(opt).

The control unit can be configured for evaluating the form of theantenna signal power resulting in response to a sequence of changes ofthe gain factor performed in tests. If then the gain factor is increasedor decreased in steps of 1 dB, for example incrementally inpredetermined variables of the gain factor, this pattern can besimilarly found again in the detected antenna signal by means of theantenna signal power, for example at the output of the antenna signalamplifier toward the antenna when the control of the mobile radioterminal on the network side is not effective. It is thus possible toreliably determine by means of a simple comparison of patterns whetheran adaptation of the gain factor is required.

The control unit can be configured for changing the gain factor in aphase in which the detected transmit signal power of the mobile radioterminal is constant. The control unit is then configured for selectinga gain factor suitable for compensating for the difference of theantenna signal power detected during this process of the antenna signalamplifier and the transmit signal power of the mobile radio terminal.The transmit signal power of the mobile radio terminal which remainsconstant despite the change in the gain factor is thus utilized asmeasure to which then the transmit signal power at the output of theantenna signal amplifier is raised by adapting the gain factor. Thisdifference is the gain, still lacking, of the permanently set minimumpreamplification (V_(min)), by which the gain must be increased in orderto obtain a precise compensation for the entire attenuation from themobile radio terminal up to the vehicle antenna.

The adaptation of the gain factor necessary for compensating for theactual coupling attenuation can thus be determined very simply from thedetected signal difference of the transmit signal power of the mobileradio terminal and the antenna signal power which is also reflected bythe change in the antenna signal output power of the antenna signalamplifier toward the antenna as a result of the change in the gainfactor. In this case, it is assumed that the mobile radio terminal isoperated with maximum known transmit power.

The control unit can be configured for the detection of the antennasignal power received from the circuit arrangement via the antenna orradiated via the antenna for the incremental change of the gain factorin a phase in which the detected antenna signal power is constant, andfor determining the coupling attenuation as a ratio or difference of thedetected antenna signal power and a predetermined maximum antenna signalpower when the incremental change of the gain factor does not lead to achange in the detected antenna signal power or the detected transmitsignal power of the mobile radio terminal.

This is so because the gain still lacking in the permanently set minimumpreamplification (V_(min)), by which the gain must be increased in orderto obtain a precise compensation for the entire attenuation from themobile radio terminal up to the vehicle antenna (i.e. the proportion ofcoupling attenuation still to be compensated for) corresponds to thequotient or the difference between the antenna signal power detectedbefore the change in the gain factor in the phase in which the detectedantenna signal power is constant, and the known predetermined maximumantenna signal power for the case that in spite of a change in the gainfactor, particularly the enlargement of the gain factor, either theantenna signal power at the output of the antenna signal amplifier or,due to the lacking effectiveness of the power control of the mobileradio terminal, the transmit signal power of the mobile radio terminaldoes not change.

The circuit arrangement can have a data memory for storing the adaptedgain factor and a predetermined minimum gain factor. The control unit isconfigured in such a way so as to read out the adapted gain factorstored in the data memory and the minimum gain factor in order to drivethe antenna signal amplifier by this means. In this context, the gainfactor of the antenna signal amplifier is set to the minimum gain factorread out, as a rule by the control unit, if the power control on thenetwork side of the mobile radio terminal is operable. Otherwise, theantenna signal amplifier is driven by the adapted gain factor. This cantake place at least by means of the adapted gain factor until a newadaptation of the gain factor is required.

The control unit can be configured for adjusting the antenna signalamplifier with the adapted gain factor for as long until a maximumtransmit signal power of the mobile radio terminal is detected. Ondetection of an operation at maximum transmit signal power of the mobileradio terminal, a new adaptation of the gain factor takes place in themanner described before. For this purpose, there can then be a test-wisechange of the gain factor again as, for example, a test-wise incrementalincrease of the gain factor and an evaluation of the resultant response.

DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail in the text whichfollows by means of an illustrative embodiment, using the attacheddrawings, in which:

FIG. 1—shows a diagram of a radio system comprising a base station and acompensation circuit arrangement, installed in a motor vehicle betweenan antenna and a mobile radio terminal;

FIG. 2—shows a block diagram of an embodiment of a compensation circuitarrangement;

FIG. 3—shows a diagram of the signal powers of the mobile radio terminaland of the antenna signal amplifier and of the gain factor over time ina power range;

FIG. 4—shows a diagram from FIG. 3 with antenna signal power of theantenna signal amplifier in the saturation range;

FIG. 5—shows a diagram according to FIGS. 3 and 4 with transmit power ofthe mobile radio terminal in the saturation range;

FIG. 6—shows a diagram from FIG. 5 with further utilization of anadapted gain factor.

DETAILED DESCRIPTION

FIG. 1 shows a diagram of a mobile radio system comprising a basestation 1 and a mobile radio terminal 3 operated in a motor vehicle 2.In the motor vehicle 2, a coupling shell 4 is installed foraccommodating the mobile radio terminal 3 which is configured via anantenna signal link 5 to a circuit arrangement 6 for compensation of thecoupling attenuation occurring in the antenna signal link 5 betweenmobile radio terminal 3 and an antenna 7 on the vehicle 2. For thispurpose, the compensation circuit arrangement 6 has an antenna signalamplifier.

In the signal path between base station 1 and mobile radio terminal 3,the following powers and losses occur:

The mobile radio terminal 3 initially sends an electromagnetic radiosignal having the transmit power Pm(jω). Then, coupling losses Ko(jω)occur due to coupling between mobile radio terminal 3 and coupling shell4. In the antenna signal link 5 between coupling shell 4 andcompensation circuit arrangement 6, further cable losses Ka1(jω) occur.

The compensation circuit arrangement 6 leads to a signal amplificationV(jω). In the antenna signal link 8 between compensation circuitarrangement 6 and antenna 7, a further cable loss Ka2(jω) occurs.

In the signal path between antenna 7 of the motor vehicle 2 and the basestation 1, there is a transmission loss G(jω). The signal power Pb(jω)lastly received by the base station 1 is thus determined not only by thetransmit power of the mobile telephone 3 but by the intermediate lossesand gains. The signal power Pb(jω) received by the base station 1 isthus calculated as follows:

Whilst the cable losses Ka1(jω) and Ka2(jω) in a vehicle 2 are constant,as a rule, the losses G(jω), V(jω) (controlled) and Ko(jω) change inoperation. For short times within a range of less than 1 ms, it can beassumed then that the coupling attenuation Ko(jω) and the transmissionlosses G(jω) do not change significantly and are virtually constant. Thegain factor for adjusting the gain V(jω), in contrast, is a parameterwhich is well controllable also within such short-time phases. If it ischanged in such short times, this influences the output power of themobile radio terminal 3 measurably due to the power control of themobile radio terminal 3 occurring which is controlled by the basestation 1. This power control on the network signal (also calledClose-Loop regulation) occurs, e.g. in the case of the LTE communicationstandard, in a periodicity of 667 μs (1500 Hz).

It can thus be seen from FIG. 1 that when a mobile radio terminal 3 isconnected to an external antenna 7 of the motor vehicle 2 as takesplace, for example, in the case of hands-free facilities in motorvehicles 2, an attenuation occurs in the signal path from the mobileradio terminal 3 to the antenna 7 and conversely. Although the qualityof transmission and reception are to be improved by the external antenna7, this attenuation does not lead to the possible achievable signalquality. In the case of an electromagnetic, capacitive or inductivecoupling of the mobile radio terminal 3 to the antenna signal amplifierof the compensation circuit arrangement 6 and the antenna 7 connectedthereto, the attenuation can vary in dependence on the current operatingstate, on the mobile radio terminal 3 used (and on the position of themobile radio terminal 3). A predetermined constant gain factor is thennot optimal and cannot achieve the required compensation especially forzones having poorer conditions of reception.

The compensation circuit arrangement 6 is then configured in such a waythat the coupling attenuation occurring between mobile radio terminal 3and antenna 7 is adapted adaptively continuously via adapting the gainfactor, i.e. the amplification V(jω) without access to information ofthe mobile radio terminal 3, i.e. without data analysis, by means of asimple continuous antenna signal power measurement (level detection) andan initialization sequence to the coupling attenuation currentlyactually present in the antenna signal link, and thus an operatingstate.

FIG. 2 shows a block diagram of the compensation circuit arrangement 6.The compensation circuit arrangement 6 has a first antenna signalamplifier 9 a for the transmit signal transmitted from the mobile radioterminal 3 to the antenna 7 and a second antenna signal amplifier 9 bfor the receive signal received via the antenna 7 from the base station1 and forwarded to the mobile radio terminal 3. To switch between thetransmit path TX and the receive path RX of the antenna signalamplifiers 9 a, 9 b, there are switches and/or filter elements 10. Afurther switch 11 can be provided for a bypass link 12 in order to passa signal without further amplification. Like the selection of the numberof antenna signal amplifiers 9 a, 9 b, this is optional possiblyseparated for individual frequency bands. Thus, separate antenna signalamplifiers can be provided in signal branches provided for this purpose,e.g. for each mobile radio system GSM, CDMA/LTE and possibly fordifferent frequency bands such as, e.g. 800 MHz, 900 MHz, 1800 MHz, 1900MHz, 2100 MHz and 2600 MHz.

To measure the signal powers, there can be, for example, a firstdetection unit 13 a for the determination of the transmit signal powerof the mobile radio terminal occurring there at the input of thecompensation circuit arrangement 6 toward the mobile radio terminal 3, asecond detection unit 13 b on the input side in the transmit path TX forthe detection of the active band and a third detection unit 13 c at theoutput of the compensation circuit arrangement 6 toward the antenna 7.By means of these detection units 13 a, 13 b, 13 c, the signal powerpresent there is detected and transferred to a control unit 14. Thecontrol unit 14 then determines a respective gain factor V1, V2, bymeans of which the current coupling attenuation determined by thecontrol unit 14 is compensated for the transmit path TX and the receivepath RX. It can be seen that possibly a number of detection units of thefirst, second and third type, i.e. of the detection units 13 a, 13 b, 13c can be present for each frequency band provided. The first, secondand/or third detection units 13 a, 13 b, 13 c can be designed formeasuring the signal powers in a number of frequency bands but alsooptionally in each case as one unit for the detection of the signallevels present in selectable frequency bands.

With the aid of the control unit 14, a further adjustment of the gainfactor V1, V2 of the at least one associated antenna signal amplifier 9a, 9 b is thus superimposed on the control loop mandatorily present inthe system, i.e. on the power control on the network side between mobileradio terminal 3 and base station 1. The power control on the networkside is determined by an antenna signal power control loop between theconnected mobile radio terminal 3 and the base station 1, connectedtherewith, of a mobile radio network, with which the mobile radioterminal 3 is in communication connection. By means of this powercontrol on the network side, a control of the transmit power of themobile radio terminal 3 is carried out by the specifications of thecommunication standard.

The control unit 14 is then configured for the attenuation compensationby suitable programming in the way described in the text which follows.

It is assumed that below a particular limit value P_(limit) for thedetected antenna signal power the reception is adequate enough and theprimary power control of the mobile radio terminal 3 on the networkside, present in any case, ensures operation within a permissible powerrange. By means of the power control on the network side, a couplingattenuation is thus compensated for automatically and completely.

This operating range is formed in the diagram in FIG. 3. The signalpower P is shown there over time t for the transmit signal power P_(M)of the mobile radio terminal 3 and the antenna signal power P_(A) at theoutput of the compensation circuit arrangement, i.e. the compensatoroutput power. Furthermore, the compensator amplification, i.e. the gainfactor V of the antenna signal amplifier is plotted over time t. Forthis range of adjustment, a minimum gain factor V_(min) is thenspecified in such a manner that the amplification within an assumedlowest coupling attenuation exactly compensates for it. By means of thedashed continued lines it is indicated that the control unit 14 isoptionally configured in such a way that it adjusts the specifiedminimum gain factor V_(min) when the detected antenna signal power P_(A)is less than the specified limit value P_(limit). This leads to thetransmit power P_(M) of the mobile radio terminal 3 always lying withinthe permissible limit up to the predetermined maximum transmit powerP_(max).

It can also be seen that the control unit 14 is configured for thetest-wise adaptation of the amplification factor V, for example in stepsof predetermined attenuation, e.g. in 1 dB steps. Thus, the gain factorV can be increased, e.g. in a number of 1 dB steps following oneanother. Due to the effective power control on the network side thisleads to the transmit power P_(M) of the mobile radio terminal 3 beingcorrespondingly reduced in order to keep the predetermined antennasignal power P_(A) constant. In the short measuring and testing time itmust be assumed that the environmental influences can be assumed to bevirtually constant.

In FIG. 4 (limit case) it is clear from the diagram with operation ofthe mobile radio terminal 3 above the predetermined limit valueP_(limit) that the power control on the network side still ensures, whenthe gain factor V is increased test-wise in the steps in the timeinterval between t3 and t4 that the antenna signal power P_(A) is keptconstant at the output of the compensation circuit arrangement 6.

Due to a test-wise increase in the gain factor V, for example in anumber of steps in succession of one another, a corresponding pattern ofthe transmit power P_(M) of the mobile radio terminal 3 can thus be seenin normal operation with operable power control on the network side withwhich the actual coupling attenuation can still be compensated forcompletely which is oppositely directed hereto.

FIG. 5 then shows a diagram of the antenna signal power P over time tinwhich the transmit power P_(M) of the mobile radio terminal 3 remainsconstantly on the value of the maximum transmit power P_(max) with atest-wise increase in the gain factor V. This makes it clear that abovea certain limit value for the detected antenna signal power P, i.e. witha poorer reception, the power control on the network side graduallychanges into the maximum transmit power range P_(max). With thecommunication according to the LTE standard, this would be the case at24 dBm. Whereas in a situation according to FIG. 4, the power control onthe network side acting with a periodicity of 667 μs (1500 Hz) can actin comparatively greater time intervals with the incremental change ofthe gain factor V, an unaltered constant value of the transmit powerP_(M) of the mobile radio terminal 3 arises when the maximum transmitpower is reached as in FIG. 5. In spite of the increase of the gainfactor V, the transmit power P_(M) of the mobile radio terminal 3 is notyet sufficient for completely compensating for the coupling attenuation.This situation is recognizable not only due to the fact that thetransmit power P_(M) of the mobile radio terminal 3 remains constant inspite of a test-wise increase in the gain factor V. On the output powerP_(A) of the compensation circuit arrangement 6, a correspondingincremental increase is also found which follows the pattern of thetest-wise change in the gain factor V directly. Thus, it is not onlyreaching the maximum transmit power P_(max) via the transmit signal ofthe mobile radio terminal 3 which can be utilized for recognizing whenthe mobile radio terminal 3 sends with maximum transmit power in orderto be able to then infer the precise coupling attenuation by means ofthe detected antenna signal power P_(A). Instead, after finding anunchanged detected antenna signal power P_(A), the amplification isincreased test-wise in steps or, if necessary, reduced and the responseof the mobile radio terminal 3 is observed. If it can be seen that thepower control on the network side is activated, this is equivalent to asufficiently good reception with the minimum amplification V_(min) beinggiven and the primary power control on the network side ensures areliable connection with compensation for the currently existingcoupling attenuation.

Should the transmit power P_(M) of the mobile radio terminal 3 still beconstant in spite of a change in the amplification V, it can be assumedthat the mobile radio terminal 3 is actually transmitting with maximumtransmitting power. The difference between the measured input powervalue of the circuit arrangement 6 and the maximum transmit powerP_(max) of the mobile radio terminal 3 then assumed is caused by thecoupling attenuation and cable attenuation. It can be used for adjustingthe optimum amplification by means of which a precise compensation wouldbe possible.

This optimum gain factor V_(opt) can be calculated with the aid of thisdifference or of the quotient or also, however, determined test by testby increasing the gain factor V. The optimum gain factor is thenpreferably deposited in a data memory of the compensation circuitarrangement 6 and read out of it for driving the antenna signalamplifiers 9 a, 9 b.

This stored value V_(opt) can then be utilized until the nextcalculation phase and retained.

This is outlined in FIG. 6. It can be seen that as a result, thetransmit power P_(M) of the mobile radio terminal 3 and the antennasignal power P_(A) at the compensator output are matched since theactual coupling attenuation is almost completely balanced with theoptimum gain factor V_(opt). If the coupling attenuation changes, forexample by displacement of the mobile radio terminal 3 on the couplingshell 4, the optimum gain factor V_(opt) can be determined, stored andadjusted in the next calculation phase, i.e. when it is detected thatthe mobile radio terminal 3 is again sending with maximum transmit powerP_(max). This ensures that the primary power control on the network sideis supported by adaptation of the gain factor V without two controlloops acting against one another. In addition, it is ensured that thecompensation circuit arrangement 6 adapts an adaptation of the gainfactor V to the attenuation actually present in the antenna signal path.

The detection unit 13 a, 13 b, 13 c is preferably implemented withrespect to signals in the circuit arrangement 6 in such a manner thatthe antenna signal power P_(A) at the output of the circuit arrangement6 of at least one associated transmit amplifier 9 a, which is used foramplifying an antenna signal sent out by the mobile radio terminal 3 isdetected. Detection of the antenna signal power P_(A) as transmit powerof the mobile radio terminal 3 has the advantage that this power of thetransmit signal is significantly higher than the power of the receivesignal in the received path RX. The change of this signal power can bedetected from the noise of the antenna signal with a good correlationwith the power control of the antenna signal power control loop betweenmobile radio terminal 3 and base station 1, i.e. detecting the powercontrol on the network side and using it as quantity utilized foradaptation of the gain factor V.

The control unit 14 can then be configured for adapting the gain factorV1 of at least one transmit amplifier 9 a which serves for amplifying anantenna signal sent out by the mobile radio terminal 3. An adjustment ofat least one associated receive amplifier 9 b, which serves foramplifying an antenna signal received via the antenna 7, e.g. from abase station 1, can then take place in dependence on the adapted gainfactor V1 of the associated transmit amplifier 9 a. The gain factor V2for the receive amplifier 9 b is thus specified, e.g. proportionallywith a specified factor to the gain factor V1. The adaptation of thegain V of the compensator thus occurs preferably on the basis of thetransmit signal of a connected mobile radio terminal 3. This adaptedgain factor V1 is then utilized directly or proportionally to theadjustment of the receive gain factor V2.

With the aid of the recognition of the response to a change of the gainfactor in the antenna signal power, it can be ensured in a simple mannerthat the actual coupling attenuation can be compensated for optimallyand it is ensured that with a maximum transmit power of the mobile radioterminal 3 the antenna signal power P_(A) does not exceed apredetermined upper limit value P_(max) at the antenna foot point.

1. A circuit arrangement for compensating for an attenuation occurringin an antenna signal link between a mobile radio terminal and anantenna, comprising: at least one antenna signal amplifier in theantenna signal link for amplifying or attenuating an antenna signal; acontrol unit associated with said at least one antenna amplifier foradjusting a gain factor by which the antenna signal conducted throughthe at least one signal amplifier is amplified or attenuated; and acircuit arrangement having at least one detection unit for detecting anantenna signal power of the antenna signal in a signal path of theantenna signal link, wherein the control unit is configured for changingthe gain factor, for detecting a change, following as response to achange of the gain factor, of antenna signal power caused by a change oftransmit power of a mobile radio terminal, and for adapting the gainfactor to a coupling attenuation of the antenna signal link independence on a detected response of the mobile radio terminal.
 2. Thecircuit arrangement according to claim 1, wherein the control unit isconfigured for a further increase in the gain factor if, by detectingthe antenna signal power, no change of the transmit signal power of themobile radio terminal as response to a test-wise increase in the gainfactor is detected.
 3. The circuit arrangement according to claim 1,wherein the control unit is configured for adjusting a predeterminedminimum gain factor if the detected antenna signal power is less than apredetermined threshold value.
 4. The circuit arrangement according toclaim 1, wherein the control unit is configured for adjusting apredetermined minimum gain factor when a change in the detected signalpower is detected.
 5. The circuit arrangement according to claim 1,wherein the control unit is configured for adjusting a predeterminedminimum gain factor when the detected antenna signal power is less thana predetermined second threshold value after the first determination ofan optimal gain factor.
 6. The circuit arrangement according to claim 1,wherein the control unit is configured for evaluating the form of theantenna signal power detected with the at least one detection unit inresponse to a sequence of test-wise changes of the gain factor.
 7. Thecircuit arrangement according to claim 1, wherein the control unit isconfigured for changing the gain factor in a phase in which the detectedtransmit signal power of the mobile radio terminal is constant, to again factor suitable for compensating for a difference of the antennasignal power detected during a process of the antenna signal amplifierand the transmit signal power of the mobile radio terminal.
 8. Thecircuit arrangement according to claim 1, wherein the control unit isconfigured for the detection of antenna signal power received via anantenna from the control unit or radiated via the antenna for anincremental change of the gain factor in a phase in which the detectedantenna signal power is constant, and the control unit is configured fordetermining the coupling attenuation in dependence on the detectedantenna signal power when the incremental change of the gain factor doesnot lead to a change of the detected antenna signal power.
 9. Thecircuit arrangement according to claim 1, wherein the circuitarrangement includes a data memory for storing an adapted gain factorand a predetermined minimal gain factor.
 10. The circuit arrangementaccording to claim 1, wherein the control unit is configured foradjusting the antenna signal amplifier with an adapted gain factor foras long until a maximum transmit signal power of a mobile radio terminalis detected, and on detection of an operation at maximum transmit signalpower of the mobile radio terminal a new adaptation of the gain factortakes place.
 11. A method for compensating for an attenuation occurringin an antenna signal link between a mobile radio terminal and an antennawith the aid of at least one signal amplifier in the antenna signal linkcomprising the steps: detecting an antenna signal power of the antennasignal in the signal path of the antenna signal link, changing a gainfactor, detecting if the antenna signal power changes in response to thechange of the gain factor due to a power control of the mobile radioterminal, and adapting the gain factor to the coupling attenuation ofthe antenna signal link in dependence on a detected change in theantenna signal power as a response of the power control of the mobileradio terminal.
 12. The method according to claim 11, further comprisinga further increase or further decrease of the gain factor when, due todetection of the antenna signal power, no change of the transmit signalpower of the mobile radio terminal as a response to a test-wise increasein the gain factor is detected.
 13. The method according to claim 11,further comprising the step of adjusting a predetermined minimum gainfactor when the detected antenna signal power is less than apredetermined threshold value or when a change of the received transmitpower is detected.
 14. The method according to claim 11, furthercomprising evaluating a form of the antenna signal power which isobtained as a response to a sequence of test-wise changes of the gainfactor.
 15. The method according to claim 11, further comprising thestep of incrementally changing the gain factor and retaining of the gainfactor over a time interval which is greater than the control time of apower control of the mobile radio terminal through control signals of abase station.
 16. The method according to claim 11, further comprisingchanging the gain factor in a phase in which the detected transmitsignal power of the mobile radio terminal is constant to a gain factorsuitable for compensating for the difference of antenna signal powerdetected during a process of the antenna signal amplifier and thetransmit power of the mobile radio terminal.
 17. The method according toclaim 1, further comprising the steps of: detecting the antenna signalpower received via the antenna or radiated via the antenna,incrementally changing of the gain factor in a phase in which thedetected antenna signal power is constant, and determining a couplingattenuation in dependence on the detected antenna signal power when theincremental change of the gain factor does not lead to a change in thedetected antenna signal power.